The present invention is directed to unitary plastic containers generally referred to as pails and mating closures, and particularly to containers having interlocking structure between the pails and closures that include mating helical threads.
Plastic containers, commonly referred to as pails, and more particularly as wide mouth or open-headed pails, are used for packaging and transporting various materials. The various materials may be solids, liquids or pastes, aqueous or organic, acidic or alkaline, e.g., detergent solutions, lattices, foods or condiments, fine chemicals, etc. The pails are typically sized to contain between three and six gallons, but other sizes are also known. Because of inertness and toughness, plastics such as high density polyethylene, polypropylene, or other inert moldable thermoplastic resins are preferred materials. The containers are filled with the desired contents, capped, stored, and shipped. During both storage and shipment, the containers are often stacked one upon the other. After being opened, they may be reopened and closed as the contents are used. When initially filled, and when subsequently reclosed, is it generally desirable for the lid to be secured sufficiently to the pail so that the lid will not separate from the pail in the event of a fall from an elevated position.
Some pails employ lids that utilize an interference fit derived from a snap on application of the lid over the open top on the pail. Such lids commonly employ an inverted U-shaped rim having weakened segments to join arcuate engaging portions of the rim to the pail top perimeter. The lid is typically separated from the pail by first breaking one or more of the segments. Once broken, the retention of the lid on the pail becomes somewhat problematic, particularly in the event of a fall from an elevated position. Other pails employ lids also with inverted U-shaped rims have integrally molded threads so that when the pail is closed, there is mating engagement outwardly of the inner leg of the inverted U-shaped rim with a corresponding thread on an outer surface of the pail opening. These constructions are known to give relatively easy opening and closing of the lid on the pail yet equal or excel the performance of conventional closed pails utilizing interference fits from snap over tops on the pails. What is needed, however, is a conveniently molded interlocking mechanism that can be used to repeatedly secure the threaded lid to the pail at a pre-selected orientation that is easily released without the destruction of any bridging segments.